Liquid chromatography-electrospray mass spectrometry of tunicamycin-type antibiotics

Several Streptomyces and Clavibacter species produce a family of tunicamycin-like antibiotics (tunicamycins, streptovirudins, corynetoxins, etc.) that inhibit the polyprenol-P:N-acetylhexosamine-1-P translocase family, thus blocking both bacterial cell wall biosynthesis and eukaryotic protein N-glycosylation. The mechanisms of biosynthesis and resistance to these toxins by the producing bacteria are largely unknown. Electrospray ionization (ESI) and matrix-assisted laser desorption ionization (MALDI) mass spectrometric techniques are described that structurally assign tunicamycin N-acylated variants in the picomolar range. A voltage gradient across the ESI inlet port was used to generate fragmentation ions that were structurally diagnostic for the tunicamycins. The application of in-line reversed-phase high-performance liquid chromatography-electrospray MS (LC-ESI-MS) resulted in the identification of eight new tunicamycins. Based on these structural assignments a revised nomenclature for tunicamycins is proposed. Application of the LC-ESI-MS methodology to culture supernatants and cellular extracts of the tunicamycin-producing bacterium, Streptomyces lysosuperificus, confirmed tunicamycin production and showed it to be growth-temperature dependent, but did not detect corynetoxins production in culture by phage-infected Clavibacter toxicus.